Synthesis of amine functional addition polymers in general is difficult for two reasons. The simplest amine functional monomer, vinylamine, is thermodynamically and kinetically unstable relative to the isomeric Schiff base and condensation products of the base, ethylidene imine. Also, more complex molecules containing free radically polymerizable functionality, e.g., olefinic groups, and primary amine functionality are more expensive and typically show severe chain transfer during radical polymerization, especially involving protons on carbon atoms alpha to the nitrogen. The allylamines are particularly good examples of this difficulty and are known to produce mainly low molecular weight polymers and copolymers, even using large amounts of free radical initiators.
Despite these problems, amine containing polymers are highly valued in a number of areas. They represent virtually the only cost effective way of incorporating cationic charge into polymers for, e.g., cationic electrocoating, water treatment and enhanced oil recovery, primary and, to a lesser extent, secondary amines offer the highest general reactivity spectrum of any group compatible with water. They will react with anhydrides, epoxides, isocyanates, esters, aziridines, aldehydes, ketones, Michael acceptors, aminoplasts and other alkylating agents to form covalent linkages. They react with acids and metal ions to form ionic linkages. Simple derivatives, e.g., Schiff bases, strongly and selectively complex many metal ions. This high reactivity produces a myriad of current and potential uses in such areas as coatings, adhesives, binders, structural polymers, viscosity control agents, ion exchange resins, and polymer boundary agents for bio/medical applications.
Because of their high electron donating ability when unprotonated and cationic charge when protonated, they offer superior adhesion to many types of substrates compared to other polymers which are typically neutral or anionic. The ability to change the reactivity and properties of primary or secondary amines by a simple pH change (addition of acid or base) offers numerous valuable options for viscosity control, emulsion stability control, polymer solubility modification (especially in water), or for formulating shelf-stable but reactive crosslinking or substrate reactive systems.
For many purposes it is desirable to prepare water soluble polymers which contain relatively low levels of amine functionality, either to reduce costs by diluting the expensive amine component or for applications in which a lower level of cationic or reactive amine gives superior performance. A particularly attractive polymer for certain applications would be a vinyl alcohol copolymer with a low but controllable level of amine functionality.
Preparation of amine functional polyvinyl alcohol (PVOH) has been previously attempted by hydrolyzing copolymers of vinyl acetate and either N-vinyl-O-t-butyl carbamate or N-vinylacetamide. The carbamate monomer is prepared by a long and costly synthesis and is reported to hydrolyze to a highly toxic aziridine in the presence of water. In both cases the poly(vinyl acetate) component was hydrolyzed with methanolic or aqueous base. In the carbamate case, treatment of an aqueous solution of the poly(vinyl alcohol)-co-poly(N-vinyl-O-t-butyl carbamate) with acid gave the poly(vinyl alcohol)-co-poly(vinylamine) acid salt. Hydrolysis of the poly(N-vinylacetamide) is known to require strong acid at high temperatures. Both approaches produce a relatively dilute aqueous solution of the polymer which is expensive to store or ship or requires expensive additional steps to isolate the polymer from the solution. The aqueous solution also contains substantial amounts of frequently undesirable salts or acid.
R. W. Stackman. et. al., Ind. Eng. Chem. Prod. Res. Dev., 1985, 24, 242 discloses copolymerization of vinyl acetate with N-vinylacetamide and copolymer hydrolysis, probably to the poly(vinyl alcohol)-co-poly(N-vinylacetamide). See R. H. Summerville, et al., polymer Reprints, 24, 12 (1983).
W. M. Brouwer, et al.; J. Polym. Sci. Polym. Chem. Ed., 1984, 22, 353 discloses copolymerization of vinyl acetate with N-vinyl-O-t-butyl carbamate and copolymer hydrolysis.